The present invention relates to transfer cases and more particularly to a transfer case having a multi-gear transfer mechanism.
Traditionally, four-wheel drive (4WD) and all-wheel drive (AWD) vehicles enable transfer of drive torque, produced by an engine and supplied through a gear reducing transmission, to front and rear wheel assemblies. Depending upon the particular vehicle configuration, drive torque can be transferred to both the front and rear wheel assemblies on a full-time basis, part-time basis or xe2x80x9con-demandxe2x80x9d basis. A vehicle using an xe2x80x9con-demandxe2x80x9d system, normally operates in two-wheel drive (2WD) driving one of the front and rear wheel assemblies and selectively transfers drive torque to the other of the front and rear wheel assemblies in response to vehicle driving conditions.
A transfer case is generally provided for enabling the split of drive torque between the front and rear wheel assemblies. The transfer case includes an input, operably interconnected to an output of the transmission, a first output shaft and a second output shaft, respectively interconnected with the wheel assemblies. A transfer mechanism is provided therein for selectively engaging the first and second output shafts, enabling the transfer of drive torque therebetween. The transfer case must be conveniently packaged within a vehicle underbody, avoiding interference with other vehicle components including drive shafts, exhaust, suspension, vehicle frame and the like. Packaging of the transfer case within a vehicle underbody has become more difficult in recent years, as automakers seek to implement 4WD/AWD systems in smaller vehicle applications.
Traditional transfer mechanisms include first and second transfer gears interconnected by a transfer chain. The transfer gears are respectively interconnected with the first and second output shafts for rotation therewith. As the first output shaft is caused to rotate, thereby rotating the first transfer gear, the transfer chain transfers drive torque to the second output shaft through the second transfer gear.
Transfer mechanism employing transfer chains retain significant disadvantages. A first disadvantage is the limited configurability. As mentioned above, a recent trend is to provide 4WD/AWD systems in increasingly smaller vehicle applications. Thus, underbody packaging plays an important role. Traditional transfer cases are sometimes difficult to properly package due to the limited configurability of the chain-type transfer mechanisms. A second disadvantage if noise, vibration and harshness (NVH) associated with chain-type transfer mechanisms.
In view of the above, it is desirable in the industry to provide an improved transfer case design. In particular, the improved transfer case design should alleviate the problems associated with traditional transfer cases employing chain-type transfer mechanism and should further enable design flexibility for resolving underbody packaging issues.
Accordingly, one embodiment of the present invention provides a transfer case for use in a motor vehicle to selectively transfer drive torque from a powertrain to first and second pairs of wheels. The transfer case includes a first output shaft driven by the powertrain and operably interconnected with the first pair of wheels for driving the first pair of wheels, a second output shaft selectively driven by the first output shaft and operably interconnected with the second pair of wheels for driving the second pair of wheels, and a transfer gear assembly operably disposed between the first output shaft and the second output shaft for transferring drive torque from the first output shaft to the second output shaft. The transfer gear assembly includes a first transfer gear in selective drive connection with the first output shaft, the first transfer gear having a first rotational axis, a second transfer gear in drive connection with the first transfer gear, the second transfer gear having a second rotational axis and a third transfer gear in drive connection with the second transfer gear and the second output shaft, the third transfer gear having a third rotational axis.
In accordance with another embodiment of the present invention, the transfer case further includes a fourth transfer gear having a fourth rotational axis and intermeshed with the first transfer gear and the second transfer gear and a fifth transfer gear having a fifth rotational axis and intermeshed with the second transfer gear and the third transfer gear. Preferably, any two of the first, second, third, fourth, and fifth rotational axis define a plane from which the other of the first, second, third, fourth, and fifth rotational axis are offset.
In either the first or second preferred embodiments, a clutch pack is preferably disposed between the first output shaft and the first transfer gear for selectively establishing drive connection therebetween. In this manner, xe2x80x9con-demandxe2x80x9d AWD is provided for.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.